This invention pertains to the preparation of aliphatic aldehydes from carboxylic acid esters of primary alcohols and more particularly to the use of a catalyst composition having a wide combination of oxidized elements.
Many methods are known in the prior art for the preparation of aliphatic aldehydes such as acetaldehyde. However, with the exception of a note by Meier and Kiefer (Angew. Chem./65, No. 12, page 320, 1953), in which ethyl acetate was converted to acetaldehyde in the presence of basic alumina and 2,4-dinitrophenylhydrazine, the literature describes no other single step process to carry out this reaction. The usual procedure would involve first hydrolysis of for example ethyl acetate to form alcohol and acetic acid. The second step would then involve the reduction of the acetic acid to ethyl alcohol and finally both mols of ethyl alcohol would have to be dehydrogenated to acetaldehyde. Of these steps the chemical reduction is expensive usually requiring a stoichiometric amount of laboratory reductant, for example, lithium-aluminum hydride. All three steps require separate isolation and purification procedures and would increase the overall cost of the preparation of acetaldehyde by this method.
The reverse reaction, the preparation of aliphatic ester from aldehyde, known as the Tishchenko reaction, is conducted using a strong base such as aluminum isopropoxide.
The teaching of Meier et al. specifically teaches that neutral and acid aluminas cannot be used for the purpose of converting ethyl acetate to acetaldehyde.
The early chemical literature teaches that ethyl acetate vapor passed over alumina at elevated temperatures affords acetone, ethylene, carbon dioxide and water. If titania is used, the products are acetic acid and ethylene. If thoria is used, acetone, ethanol, ethylene, and carbon dioxide are formed. (H. Adkins et al., J. Am. Chem. Soc., 44, 385, 1922).
In the presence of nickel and 300.degree.-450.degree. C., ethyl acetate is decomposed to carbon monoxide, carbon dioxide, hydrogen and methane (H. Adkins, Ibid, 44, 2175, 1922).
Bancroft et al. found only ethylene and carbon dioxide when ethyl acetate was passed over alumina (Ibid. 35, 2943, 1931).
When ethyl acetate is oxidized with oxygen in the presence of cobalt naphthenate, the only product is acetic acid in a yield of 80-90% (U.S. Pat. No. 2,530,512; British Pat. No. 643,468, 1950).
When certain oxide catalysts, e.g., CuO,80:Cr.sub.2 O.sub.3,10, are used, oxidation of ethyl acetate at 130.degree.-235.degree. C. in the presence of steam leads only to complete combustion to carbon oxides and water (V. S. Saltanov, Khim, Prom. 44 (5), page 349, 1968; R. P. V. Subba Rao, Zeit. Phys. Chem., 246 (5-6), page 352, 1971).
Fish et al. (J. Chem. Soc. 1963, page 820) indicate that aldehydes are minor products, with acids the major product formed in the noncatalytic (free-radical) oxidation of ethyl acetate. The only reference to a derivative of acetaldehyde as a major product is that of Meier et al. previously cited. In this process not acetaldehyde, but its 2,4-dinitrophenylhydrazone is produced in the absence of reacting oxygen. Formation of this derivative provides the driving force for the reaction and permits a higher, but still very low conversion of ethyl acetate than occurs in its absence.
It is therefore an object of this invention to provide a method for making acetaldehyde and other aliphatic aldehydes from the corresponding aliphatic esters of carboxylic acids in a one-step process which is commercially feasible.
Other objects will become apparent to those skilled in the art upon a further reading of the specification.